Excimer laser micromachiningExcimer lasers produce relatively wide beams of ultraviolet laser light. One interesting application of these lasers is their use in micromachining organic materials (plastics, polymers, etc). This is because the excimer laser doesn't remove material by burning or vaporising it, unlike other types of laser, so the material adjacent to the area machined is not melted or distorted by heating effects.When machining organic materials the laser is pulsed on and off, removing material with each pulse. The amount of material removed is dependent on the material itself, the length of the pulse, and the intensity (fluence) of the laser light. Below a certain threshold fluence, dependent on the material, the laser light has no effect. As the fluence is increased above the threshold, the depth of material removed per pulse is also increased. It is possible to accurately control the depth of the cut by counting the number of pulses. Quite deep cuts (hundreds of microns) can be made using the excimer laser. The shape of the structures produced is controlled by using a chrome on quartz mask, like the masks produced for photolithography. In the simplest system the mask is placed in contact with the material being machined, and the laser light is shone through it (figure 16a). A more sophisticated and versatile method involves projecting the image of the mask onto the material (figure 16b). Material is selectively removed where the laser light strikes it.
 Figure 16. Structures with vertical sides can be created. By adjusting the optics it is possible to produce structures with tapered sidewalls (figure 17).
 Figure 17. Excimer lasers have a number of applications beyond those mentioned here. One area of application is in machining the cornea of the eye to change its optical properties; correcting for short sight. |